Shimon Sakaguchi is a Professor at the Immunology Frontier Research Center (IFReC) at Osaka University, Japan. He is an immunologist recognized particularly for his discovery of regulatory T cells, an indispensable constituent of the immune system for the maintenance of immune self-tolerance and homeostasis. Sakaguchi obtained an M.D. in 1976 and a Ph.D. in 1982 from Kyoto University, Japan, where he was trained as a pathologist and immunologist. After performing postdoctoral studies at Johns Hopkins University and Stanford University as a Lucille P. Markey Scholar, he served as an Assistant Professor in the Department of Immunology at the Scripps Research Institute. He returned to Japan in 1991 and continued his immunology research as the Head of the Department of Immunopathology at Tokyo Metropolitan Institute of Gerontology, Tokyo. From 1998 to2011, he was a Professor of Institute for Frontier Medical Sciences Kyoto University and served as the Director of the Institute for several years. In 2011, his lab moved to Osaka University. He was elected to Foreign Member of National Academy of Sciences USA in 2012, and has been awarded with many international prizes including Canada Gairdner International Award in 2015.